ST. PAUL, Minn. (AP)  Keeping wild waterfowl from spreading bird flu to Minnesota turkey farms won’t be easy, the state veterinarian said as officials announced the sixth and seventh cases of the disease in the country’s top turkey-producing state.

Officials say it’s too early to speculate whether the highly pathogenic strain could hurt Minnesota’s $750 million turkey industry. More than 40 countries banned poultry imports from Minnesota last month, when the first case was reported, though some have since narrowed the bans to poultry from affected counties. Health officials have said the risk to the public from the virus is low.

“As far as stopping this connection between the waterfowl and turkeys, it will be a challenge this year,” Hartmann said.

There’s no evidence the H5N2 strain spread between the seven Minnesota farms infected over the past month, Hartmann said. That means wild birds such as ducks and geese, which can carry the flu but aren’t sickened by it, could be responsible.

State workers will sample wild waterfowl droppings around the infected farms to test for the virus, said Michelle Carstensen, wildlife health program supervisor at the state Department of Natural Resources. They’re also watching for any reports of dead turkeys or birds of prey in the wild.

The state will also continue to monitor any poultry farm workers who had extensive contact with infected birds, said Joni Scheftel, public health veterinarian at the Minnesota Department of Health. She stressed that the public is “absolutely not at risk.”

Three turkey farms where infections have happened are in Stearns County, in the south-central part of the state. The newest infected flock had about 76,000 birds. Neighboring Kandiyohi County had its first outbreak reported Monday in a flock of about 26,000 turkeys. State law prevents officials from disclosing the exact locations.

The H5N2 strain has resulted in the deaths of more than 300,000 Minnesota turkeys, including birds that farmers killed as a precaution. Minnesota turkey farmers raise about 46 million birds annually, according to the Minnesota Turkey Growers Association.

Hartmann said the virus thrives in the kind of cold, wet climates common in Minnesota during the spring migratory season. It has also surfaced in Kansas, South Dakota, Arkansas and Missouri.